FIG. 1 schematically illustrates one known laser heating system for joining two polymeric sheet materials S1 and S2 together. In such a system, as is conventionally known, two polymeric sheet materials S1 and S2 can be welded together if: (a) one layer S1 of material is highly transmissive to the laser energy (from laser beam LB), and (b) the other layer S2 of material is highly absorptive of the laser energy (or is otherwise treated to be highly absorptive of the laser energy). In this system and method, as the laser absorptive sheet S2 heats up, it melts the polymeric materials at the junction of the transmissive and absorptive materials, causing the two layers to melt together and thereby be “welded” together.
There are some issues with this technique. For example, for clear polymeric sheet materials, one of the two sheets (S2 in the example of FIG. 1) has to be treated in some manner so as to become more laser energy absorptive. This may be accomplished, for example, by doping the sheet material S2 with a laser absorptive material. The dopant, however, may affect other electromagnetic transmission properties of the sheet member (e.g., its color, opacity, etc.). As another example, a polymeric sheet member (e.g., S2) can be made more laser absorptive by applying a laser absorptive material 10 to a surface of at least one of the sheet materials at the desired joining location (e.g., by printing or otherwise coating a laser absorptive material on a surface of the sheet material). One such laser absorptive material 10 for this type of process is a near infrared absorbing material known as CLEARWELD®, available from Gentex Corporation. As noted above, in this method, as the laser absorptive sheet S2 heats up (shown by the heat arrows in FIG. 1), it melts the plastic material of both sheet members S1 and S2 at the junction of the transmissive and absorptive materials, causing the two layers to melt or stick together and thereby be “welded” together.
The use of such near infrared absorbing materials on the plastic sheets, however, significantly increases the costs, time, and difficulties involved in joining two polymeric film or sheet materials together. Moreover, it introduces a foreign material within the joint.
Other systems and methods for joining two plastic sheet materials together are described in U.S. Pat. No. 3,384,526, which patent is entirely incorporated herein by reference. This system uses a broadband heat lamp source with heat absorbing materials (such as graphite paint) provided on a work support in order to produce a weld.
There is room in the art for improvements and advances in systems and methods for joining polymeric materials (such as polymeric films or sheet materials) together, particularly in instances wherein the polymeric materials to be joined are substantially transparent to radiation over the visible wavelength spectrum or at least a portion of the visible wavelength spectrum.